This invention relates to a gas generator, in particular a tubular generator for an air bag, with an outer tube and an inner tube and for accepting a gas-producing material, wherein the inner tube, forming an annular intermediate chamber, is arranged radially spaced from the outer tube; with closure covers for closing open front ends of both tubes and with an ignition device, extending up to the interior of the inner tube, for igniting the gas-producing material; the ignition device being arranged centrally of the tubes.
A similar tubular gas generator is known from DE-39 14 690 C2. The known gas generator has an outer tube, in the wall (jacket) of which there are arranged gas outlet openings and the front ends of which are closed by disc-like closure covers inserted into the outer tube. Arranged coaxially to the outer tube and in this tube there is an inner tube, also provided with gas outlet openings in its jacket, the outer diameter of which is smaller than the inner diameter of the outer tube, so that there is a radial spacing between both tubes. In the annular intermediate chamber there is arranged a filter material. The inner tube, the axial length of which is less than that of the outer tube, is filled up with (pressure) gas-producing material (in the following description, this material is also called pressure gas-generating charge, for example in the form of pellets), which is ignited by an ignition unit. The gas formed upon ignition of the gas-producing material passes via the gas outlet openings of the inner tube through the filter material, in order to emerge outside via the gas outlet openings in the outer tube. The gas generator is arranged in a housing which is open on one side, when it is used for an air bag, said opening being closed by a folded fabric, the actual inflatable air bag. In this known tubular gas generator the ignition unit is arranged at one end of the gas generator in the closure cover. This "one-sided" arrangement of the ignition unit is disadvantageous with regard to a steady ignition of the pressure gas-generating charge.
A more steady ignition of the pressure gas-generating charge could be achieved, if the ignition unit was arranged in the center of the charge, at both sides of the ignition unit, located therefore, in approximately the same quantity and distribution of gas-producing material. Such arrangements of the ignition units of gas generators are known from U.S. Pat. No. 4,437,681 and U.S. Pat. No. 4,561,675. According to the latter U.S. patent, the ignition unit is arranged transverse to the longitudinal extent of the gas generator in the center of its longitudinal extent, wherein the ignition unit is anchored or secured in the relatively thick housing wall. The problems of securing the ignition device in the wall of the outer tube of a tubular gas generator consists in that this connection cannot be formed to be sufficiently stable, since the outer tube, just like the inner tube, is relatively thin, therefore a secure support, which is acting reliably against the forces produced with ignition of the charge, is not able to be achieved.